This application relates to a relief valve used to relieve pressure in a pressurized fluid system. The novel relief valve is described in this application for purposes of illustration and explanation as being installed on a water heater shutoff/thermal expansion control valve such as an Apollo® 78LF-RV Series valve manufactured by Conbraco Industries, Inc. of Matthews, N.C. However, the relief valve has application in a wide variety of uses, and its description in this application installed on a specific device carries no implication that its use is limited to use on that device.
Conventional relief valves include a body that is positioned in fluid communication with a pressurized fluid system, for example a shutoff valve, backflow valve, or pipe. A spring-loaded rubber ball bears against the walls of a relief port in the valve, pipe, etc. The spring is designed for a specific relief setting. If pressure in the system exceeds a predetermined value, that excessive pressure exerts sufficient force against the ball to unseat it from the relief port walls, allowing fluid to flow past the ball to atmosphere, an expansion tank or other reservoir. As the pressure is reduced, the ball is again urged back into sealing contact with the wall of the relief port. The spring is mounted in a conduit in the relief valve and is held in an aligned position by the walls of the conduit and a shoulder of reduced diameter against which the end of the spring remote from the ball resides. These prior art relief valves are prone to delivering inaccurate performance as a result of the spring being compressed during an over pressure event to the extent that the coils contact each other and the spring becomes, in practical effect, a solid object that restricts fluid flow from the valve. This condition can result in false pressure readings, delayed pressure relief and similar conditions.